devil weed; Sargassum horneri
A type of brown seaweed found along the coasts of Japan and East Asia. Often used in local cuisine and as a health food.
Devil weed is popular as an ingredient in miso soup.
In spring, a lot of devil weed washes up on the shore.
Kanji spelling; rarely used in practice.
The name アカモク (akamoku) likely derives from 赤 (aka, 'red') and 藻屑 (moku, 'seaweed scraps'), referring to the reddish-brown color of the seaweed. The exact historical derivation is uncertain.